1997-06-13_REVISION - M1981302 (56)

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Page 8 Comment: "This would include excavation and extension of drainage channels parallel to the existing flood control levee surrounding the Deepe Pit. As you may be aware, many concerns have been recently raised about the accuracy of the existing floodplain delineations and the impacts that the embankment and sand and gravel mining reclamation may have on the South Boulder Creek floodplain." "We have requested that the Federal Emergency Management Agency (FEMA) withhold certification of the existing embankment as a flood protection levee pending the determination of the most appropriate flood mitigation measures for this area. Since the issue of internal drainage is one of the primary FEMA criteria for evaluating the suitability of a flood control levee, we would also request that the approval of an amendment affecting internal drainage also be withheld." Response: FEMA's concerns with internal drainage of levee systems rise from the fact that areas behind levees are often subject to retention of runoff that would have otherwise flowed into the river or stream had it not been blocked by the levee system. Internal drainage problems can be severe, when dealing with the extensive levee systems that have been installed in some locations in the United States, such as the levee systems along the Mississippi River and its tributaries. Internal drainage of the approximately 6000-foot long perimeter levee at the Deepe Farm Pit does not pose a technically difficult problem, and it is not a basis for withholding approval of the Deepe Farm Pit amendment AM-002. This position is only reinforced by the fact that drainage of the Deepe Farm Pit permit area is routed to the same location at the north permit perimeter under both the existing approved plan and the plan proposed in the amendment. Comment: "All parties who are familiar with the South Boulder Creek hydrology and floodplain agree that the alluvial floodplain that includes the Deepe Farm Pit has complex and as- yet unpredicted flood behavior. All agree that the land contours of the pit(including the berm) have floodplain implications with serious health and safety consequences. All are aware of the current floodplain study by Taggart Engineering under the auspices of Urban Drainage and Flood Control District that is addressing flood hazard mitigation. The study is scheduled for completion in September, 1997. Without the results of this study, the floodplain implications of the berm can not be properly addressed. And current acceptance of the berm and amendment topography would cripple the ongoing floodplain planning process by predetermining important land contours." Response: Delineation of the one percent annual chance floodplain around the Deepe Farm Pit, if the existing perimeter levee is certified by FEMA, would be essentially the flood inundation area mapped in the 1986 Greenhome and O'Mara, Inc., Flood Hazard Delineation. The "as-yet unpredicted flood behavior" referenced by Dr. Bunin occurs in the area north of the Deepe Farm Pit where overbank flows, during the one percent annual chance flood, on the west side of South Boulder Creek would approach the